Avoid Video Flicker: Understanding PAL (50Hz) & NTSC (60Hz)

We were recently hired to produce a short documentary piece intended for broadcast in China. The project is to be shot and edited here in Canada, and later sent to China. The shooting specs for this project are as follows: 1080i50 in a .mov wrapper. Seems simple enough. We’ll go ahead and switch our camera’s mode from NTSC (60Hz) to PAL (50Hz), and we’re ready to roll! Right?

Unfortunately, it’s not that simple. Because we’re shooting for PAL in an NTSC area, it is important that we understand why NTSC and PAL standards exist in the first place. Until recently, I thought PAL and NTSC standards were simply a matter of preference, sort of like America’s Imperial system vs. UK’s Metric system. However, that is not the case at all. As it turns out, there is a very tangible reason for the opposing NTSC and PAL standards.

50Hz vs. 60Hz, a Little History

In the UK, Africa, Australia, most of Asia and Russia, the frequency of AC (alternating current) running through electrical mains is 50Hz (Herts). While in North America, and a few other countries (Japan uses both), the AC frequency is 60Hz. Why? There are many historical factors responsible for this divide but, in a nutshell, it comes down to economics. At the turn of the 21st century, to avoid competing with one another, manufacturers in America focused on producing 60Hz equipment while manufacturers in the UK focused on producing 50Hz equipment. Each region established its own monopoly and the rest is history.

It’s worth mentioning, 50Hz & 60Hz are not arbitrary frequencies. They were chosen for very specific reasons that go beyond the scope of this blog. But, to provide some perspective into it, certain lights tend to flicker when a low frequency current is run through them. If the frequency is sped up to 50Hz, the flickering, although still present, goes unnoticed by the human eye. This is one of the contributing factors to the popularity of 50Hz.

How does Household Electrical Frequency affect Video?

As mentioned, at 50Hz the flickering effect goes unnoticed by the human eye – the key word being human. The camera’s eye (its sensor) can still see this flicker. The sample footage below was shot in PAL, 1080i50, 1/50 shutter speed, at a school in Edmonton, Canada with 60Hz florescent lighting. While our camera operator was seeing a clean, flicker-free image, the camera itself was seeing something entirely different. Notice the grain and flickering effect over the dark blue curtain. Thankfully it was just a test shot!

What caused this flickering effect? Blame the hertz! (not really). The hertz is a unit of frequency that defines cycles per second. So, if the lighting in the school is running at 60Hz, this is just a fancy way of saying that the electricity flowing into the fluorescent lighting is cycling ON-OFF 60 times per second. While the human eye does not detect it, there is a subtle dimming of the light during each of these ON-OFF cycles. It is this dimming that our camera is seeing, and recording.

How to Prevent Flicker in your Video

It all comes down to synchronization. If you synchronize your camera to the electrical frequency of the lighting, you are basically telling your camera to only take pictures of the ON portion of each cycle within the frequency. So how do we do achieve synchronization? There are two options:

1. Change Your Camera’s Frequency Setting (NTSC or PAL)

Thankfully, many cameras today have the option to change frequencies between 50Hz (PAL) and 60Hz (NTSC). If your camera has this option, simply match your camera’s frequency with the electrical frequency of your environment. Once set to the correct frequency, you can safely use any of the frame rates or shutter speeds your camera offers. If you’re not sure what the frequency is where you are, here’s the Wikipedia link!

2. Change your Shutter Speed/Angle

If you can’t change your camera’s frequency, or if your client requires you to shoot in a specific frequency, as is the case for us, there is a workaround. You can sync your shutter speed to the electrical frequency of your environment. I created a couple tables below with some commonly used frame rates and corresponding safe shutter speeds/angles. If you don’t see what you need in the tables, you can use this handy shutter speed/angle calculator courtesy of the team at Red.

Shooting under 60Hz Lighting (North America)

Your Frame Rate

Safe Shutter Speed

Safe Shutter Angle

60p/60i

any

any

30p

any

any

24p

any

any

50p/50i

1/60, 1/120

300, 150

25p

1/40, 1/60, 1/120

225, 150, 75

Shooting under 50Hz Lighting (most of Europe & Asia)

Your Frame Rate

Safe Shutter Speed

Safe Shutter Angle

60p/60i

1/100

216

30p

1/33.3, 1/50, 1/100

324, 216, 108

24p

1/33.3, 1/50, 1/100

259.2, 172.8, 86.4

50p/50i

any

any

25p

any

any

The sample footage below was shot on the same day, under the same 60Hz lighting, as the sample footage above. The camera was still in 50Hz mode (1080i50), however we adjusted our shutter speed from 1/50 to 1/60 to match the frequency of the fluorescent lighting. As you can see, the results are much better!

35 Comments

Great article. It’s worth noting that LED lights can also be particularly problematic since they have a refresh rate similar to computer monitors which is a different problem than just the AC cycle. Also, different lights can flicker at different rates, so if you’re not confident about the quality of your lights, it’s really important to do tests and view them on a monitor (as your article points out).

If you do have footage that suffers from flicker, we develop a plugin that removes most types of flicker including the flicker shown in the example caused by the camera being out of sync with the electricity. It’s called Flicker Free and you can find more info here: http://www.digitalanarchy.com/Flicker/main.html

I’m researching flicker rates of different light sources for the common use. I found several studies that provide correlation between flickering light bulbs and health problems. Could someone suggest how to tell which bulb is made from a higher quality materials, flicker free? How to test which bulbs are flicker free? Is there a way of reducing this flicking? Does electromagnetic interference most highly generated by CFL correlate with the flicker rate?

Hello Jim, I apologize for the late response. I would look into Remote-Phosphor Lighting. As far as I know, it’s a relatively new lighting technology, at least in the video production world. Remote phosphor lighting is virtually flicker free due to its extremely high cycle. I believe it ranges somewhere around 250,000 Hz and up. Hope that helps with your research.

Just returned from Ukraine, shooting 23.98 fps but in one interview we accidentally let the shutter speed default to 1/48 instead of setting it at 1/100. Now of course we have a slow rolling light/dark area through the picture.

We just shot a sequence in a fabrication shop for a corporate video and the welding machines must have been on a different frequency because we ended up with some bad flickering. We used the Flicker Free Plugin by Digital Anarchy and it took all the flicker out beautifully. Can’t say enough about this plugin. It’s great. We just dropped it on our footage, left all the default settings, rendered, and the flicker was gone. It didn’t degrade the footage either. The plugin is $149 but well worth it. You can try the demo version first to make sure it works, which is what we did. Hope that helps!

Yes, PWM (Pulse Width Modulation), another term for the on-off cycling of current to an electrical device (i.e. computer monitors), causes flicker if its frequency is out of sync with your camera’s frequency/shutter. Match your camera’s frequency/shutter and flicker goes away.

Awesome post! I found this out the hard way too after doing a shoot in Australia and shooting under florescent lights while shooting NTSC. Thanks for sharing your experience – I’m going to share this with the team as it’s a great description of the problem in general.

I think you should add that 50hz wasn’t a problem for incandescent bulbs since they have rather high persistence, but the flicker from a 50hz CRT display is easy for most people to notice, even without interlacing. 60Hz, while better, still flickers enough to be annoying to people who spent long hours working on computers, thus the preference for some to set their vertical refresh rate to 72 or 75Hz.

HI
I’m planing to shoot in Pal area in few days. most my gears are NTSC. I wanna keep the same sittings i usually use here in the USA and also use the same lighting system i used in the USA. Do you think this idea will help me to avoid Flicker?

Hi! We have a DP shooting a story for us in Japan where light bulbs work both at 50 and 60 hertz. However, we’re shooting at 23.98p, will she have the same problem or the flicker only affects when shooting interlaced?

Hey sorry for the late response, hope it’s not too late. Shooting interlaced has nothing to do with it. If there are any 50 herts bulbs in the room she’ll definitely need to adjust her shutter speed to avoid flicker.

Hi there – I’m afraid my experience doesn’t match your table. I recently shot an event here in Australia (50Hz cycle) on 25p, using 180.d shutter angle. The rolling horizontal banding was TERRIBLE. I tried adjusting the shutter both up and down and the effect was still visible, so I came away with awful footage. What caused this and what should I have done? Thanks for any tips!

Hi Sarah, my apologies for the late reply. I’ve been working out of town. Is there any way I could see a sample of the footage? To be honest, if you were shooting in the correct frequency and tried various shutter angles with no luck, then I’m at a loss. The only guess I can muster up is that there were some lights at the event running on another frequency.

Hi great info. Wonder if you could help? I’m wanting to design some DIY LED camera lighting that I can dim, but I can’t get my head around how to avoid lowering the duty cycle frequency without causing camera flicker. Is there a min frequency where syncing is no longer important or relevant say for eg above 26Khz? I guess I’m wanting to find out the minimum frequency I can dim down to (eg 10% duty cycle) without risk of flicker on camera across it’s various most common settings ? Thanks for any guidance.

Sorry I didn’t get back to you sooner. Unfortunately, I literally know nothing about that stuff. I just know what settings to use in-camera to avoid flicker. Beyond that, I’m pretty useless. Good luck with the DIY project though!

hi,
i got a flicker with 30fps, 1/25 shutter speed and 50hz light. and the flicker effect reduced when i changed shutter speed to 1/50. but still flickering is there slightly, how can i avoid it completely.
I changed the sensor ROW TIME for getting fps properly on live stream earlier.
is it have any relation for this row time because this was the relation between ROWTIME and eshutterspeed
regAddr = AR0331_COARSE_IT_TIME_A;
regValue = (float)(eshutterInUsec/ROW_TIME);
does it have eny effect on flickering in video

I would need more specific info to give you proper advice (i.e. what frame rate your client wants you to shoot in and what kind of lighting you’ll be using), but I think a good starting point would be to put your camera in 60Hz mode and change your shutter speed to 1/50. If that doesn’t work, just experiment with different shutter speeds until the flicker is gone. Hope that helps!

I would like to add one thing to this already excellent article by saying that fluorescent lights near the end of their life will flicker at slower and slower speeds before fully breaking down. It is actually possible to see the flickering of the light at the very, very end of the life of a fluorescent light with the human eye. The light in particular needs replacement at this point.

It can be very frustrating when you are tinkering with your camera to get the best video quality while it is actually one or multiple of the fluorescent lights which are in dire need of replacement.

Great article, thank you. But I am confused about something:
I adjusted the settings as you suggested and my room lights and monitors are perfectly synced. But my backlit keyboard is totally out of sync. How can this be possible? Thank you.

This is a helpful page, but I have a stupid questions.
Is it possible that If I synchronize your camera to the electrical frequency of the lighting, and camera to only take pictures of the OFF portion of each cycle within the frequency, because the frequency of the light is keeping light and dim cycle. I may have some knowledge misunderstanding if so please tell me. Thanks a lot!

Hi thanks for the article. Some camera offer both flickering reduction (to be set to 50/60Hz) AND the choice of PAL/NTSC. Do you think both 50/PAL 60/NTSC should be aligned or is there something I miss ?

Hi there. I want to confirm this – I will be traveling to Italy from the US for vacation. For my trip, I should change to PAL and the corresponding fps options (I like 60fps in the US to be able to slow footage down – so 50fps in PAL, right?). When I come back, I can put all of this footage into Premier Pro and it will work well together? If I happen to video some clips at the US airports – then I need to keep my shutter speed at 1/120 for 50fps to prevent banding, right? And, can you please explain what the shutter angle is – ie, you recommendation is: 300, 150. Thank you.

You are exactly right. One thing to consider though. If you’re planning on just throwing the project on Youtube it would be easiest to shoot the whole thing in PAL mode since Youtube takes both NTSC and PAL. However, if you want to be able to watch the final video on your 60Hz TV then you might consider shooting everything in NTSC mode and just changing your shutter speed accordingly, i.e. if you shoot at 60fps, use a shutter speed of 1/100 (216-degrees). If you shoot any 24fps stuff, you would use a 1/50 shutter speed (172.8-degrees). As far as I know, there aren’t many issues viewing PAL content on an NTSC TV but it’s something to consider I guess.

Regarding the US airport, you are right. If you’re in PAL mode at a US airport, a 1/120 shutter speed will work perfectly for 50fps stuff. If you shoot any 25fps, a shutter speed of 1/60 would be best.